This application claims priority to German Patent Application Serial No. 100 40 582.7-45, filed Aug. 15, 2000, entitled xe2x80x9cPorosierender, erstarrungs beschleunigender Bindemittelbaustoff-Zusatz und Verfahren zu seiner Herstellung.xe2x80x9d
1. Field of the Invention
The invention relates to a porosifying, solidification-accelerating additive for binding agent building materials.
2. Description of Related Art
From DE 196 44 654 A1 there is known a processed salt slag of the following composition: Al2O3=65.7%; SiO2=7.9%; Fe2O3=1.5%; CaO=3.2%; MgO=10.1%; TiO2=0.9%; MnO=0.3%; Na2O=0.8%; K2O=0.4%; SO3=0.5%; F=1.2%; P2O5=0.1%; H2O=7.3. Such a powder with the crystalline phases of corundum xcex1-Al2O3, bayerite Al(OH)3, spinel MgAl2O4, and xcex1-quartz SiO2 is processed together with limestone meal at 1150-1300xc2x0 C. to form sulfo-aluminate clinker. A similar process of producing aluminate cement clinker is known from DE 43 45 368 C2.
For certain applications it is necessary to use porous inorganic binding agent building materials, which are produced with the help of the following additives:
1. Natural or synthetic porous filler materials, such as pumice, pearlite, expanded clay, plastic foam granulate
2. Organic foaming agents, e.g., surfactants or proteins
3. Gas-forming substances, e.g., aluminum powder
For producing gas concrete, it is possible to make use of the reaction of aluminum powder with lime (calcium hydroxide), which leads to the formation of hydrogen gas, as a result of which the hardening mixture of sand, cement, lime, and waterfoams up. Aluminum powder is produced by fine-grinding aluminum metal, but there exists a risk of explosion.
From DE 43 19 163 there is known a spinel-containing solid substance that is bonded by cement and which contains a high-alumina filler material. A porosifying effect of said filler material is not identifiable.
For the solidification behavior there are used additives such as calcium chloride, sodium carbonate, and calcium aluminate that are able to accelerate solidification. Other additives for delaying the solidification behavior are also known.
The invention relates to a porosifying, solidification-accelerating additive for binding agent building materials consisting of Al2O3, 50-90%; MgO, 4-20%; SiO2, 0.5-15%; AlN, 0.1-5%; Fe2O3, 0.1-5%; CaO, 0.1-5%; F, 0.1-5%; Na2O, 0.1-5%; K2O, 0.1-2%; as well as in the form of metallic particles: Al, 0.1-10%; Si, 0.1-3%; Fe, 0.1-3%; balance in total maximum, 5%; annealing losses, 0.1-15%; and of at least one mineral main constituent in the form of corundum (xcex1-Al2O3) and spinel (MgOxc3x97Al2O3). The invention also relates to a process of producing the additive for binding agent building materials.
It is an object of the present invention to provide a high-alumina additive for binding agent building materials or a respective powder and to design same in respect of its structure and composition in such a way that the additive or powder has a porosifying or accelerating effect in inorganic binding agent building materials such as light mortar, porous concrete, insulating foam, and other insulating materials.
In accordance with the invention, the objective is achieved by the characteristics as recited in the claims.
Surprisingly, it has been found that a powder with a high alumina content, which powder can be recovered from the high-alumina residue remaining when processing, especially wet processing, aluminum slag, can be used as a porosifying additive for inorganic binding agent building materials if the metallic aluminum contained in the powder is activated by thermal treatment (drying and partial calcination). The formation of pores can be controlled by the degree of thermal activation. Said additive is additionally advantageous in that the powder at the same time acts as a lean substance or volume forming agent. It is also advantageous in that it is possible to avoid the use of explosive aluminum powder as a volume-forming agent.
The activated porosifying and high-alumina powder in accordance with the invention is characterised in that it comprises:
1. As chemical constituents: Al2O3, 50-90%; MgO, 4-20%; SiO2, 0.5-15%; AlN, 0.1-5%; Fe2O3, 0.1-5%; CaO, 0.1-5%; F, 0.1-5%; Na2O, 0.1-5%; K2O, 0.1-2%; as well as in the form of metallic particles: Al, 0.1-10%; Si, 0.1-3%; Fe, 0.1-3%; balance in total maximum, 5%; annealing losses, 0.1-15%;
2. As mineral main constituents corumdum (xcex1-Al2O3) and spinel (MgOxc3x97Al2O3) and transition modifications from aluminum hydroxide (Al2O3xc3x973H2O) to xcex1-aluminum oxide, and as a subsidiary constituent aluminum metal;
3. A particle size of at least 90% smaller than 500 xcexcm; and
4. A specific BET surface of at least 10 m2/g.
The activated porosifying high-alumina powder can be recovered in that alumina-containing residual substances from the wet processing of aluminum salt slag are dried at temperatures of 1000xc2x0 C. and partially calcinated. Partial calcination means that, on the one hand, the stage of thermally removing only the physical residual moisture has already been passed, but that on the other hand, there still exist percentages of substances that can be thermally vaporized, such as fluoride out of calcium fluoride and crystal water out of aluminum hydroxide/aluminum oxide transition modifications, as well as metallic aluminum.
It is important that the drying and partial calcination of the alumina-containing residual substance is effected by devices that permit a rapid transition of heat to the product, with electric driers, cyclone calcinators, or fluidized-bed calcinators being given preference. In a rotary kiln, heat transition is slower and less uniform, so that the activation success is reduced. Furthermore, in the rotary kiln there occur agglomerates that can only be eliminated by crushing.
The subsequent examples explain the subject of the invention.